In the recovery of petroleum from subterranean formations, a bore hole is formed into the earth and through the producing formation. Production casing is run into the completed bore hole and is cemented in place. The casing is then perforated to provide communication between the producing formation and the interior of the casing.
In many instances there is initially sufficient formation pressure to cause the petroleum to flow from the producing formation upwardly through the casing to the surface. As the formation pressure is gradually reduced, it eventually becomes advantageous to employ artifical lift to enhance the flow of petroleum from the formation. One of the most commonly used types of artificial lift apparatus is known as a down hole pump.
A typical down hole pump includes a standing valve mounted at the bottom of a string of well tubing which extends downwardly from the surface. A traveling valve is mounted for reciprocation within the well tubing, and is connected to the familiar walking beam type of pumping apparatus by a series of sucker rods. Upon actuation of the walking beam pumping unit, the traveling valve is reciprocated relative to the standing valve to effect pumping of petroleum out of the producing formation and upwardly to the surface through the well tubing.
It is known that gas pressure exists within the well casing. If this pressure is above a certain level, it will cause the down hole pump to stop functioning (i.e., the pump will gas lock). When this happens, the flow of oil from the well is stopped or at least substantially impeded. On the other hand, if the gas pressure within the casing is reduced below a certain level, the flow of oil from the well will be reduced. It is believed that the reduced pressure causes the gas within the petroleum to vaporize. This vaporization causes a foaming action which substantially impedes the proper functioning of the down hole pump. Therefore, in order to optimize production, it is imperative that the gas pressure in the well be maintained within a certain range. The gas pressure which optimizes production depends on such factors as the depth of the well, the level of the fluid in the well, and the normal gas pressure within the well. The optimum gas pressure range will obviously vary from well to well.
It is commonly known that applying an uncontrolled vacuum to the well will relieve the gas pressure. This is currently accomplished by simply attaching a vacuum pump directly to the well casing. There are three problems with this. First, the gas within the well contains a certain amount of water vapor. When the surface temperature is lower than the temperature within the well, the vapor will condense into water. The vacuum pump will eventually be ruined if the water or water vapor passes through it. Second, the gas pumped from the well is simply vented into the atmosphere. This gas is a valuable energy source and should be collected, not wasted. Third, the vacuum is not controlled and will reduce the well pressure below the optimum level. As discussed previously, this will impede the proper functioning of the pump and reduce the flow of oil from the well.